This invention relates to an improved process for selectively removing hydrogen sulfide from gaseous streams.
The removal of sulfur from fluid streams can be desirable or necessary for a variety of reasons. If the fluid stream is to be released as a waste stream, removal of sulfur from the fluid stream can be necessary to meet the sulfur emission requirements set by various air pollution control authorities. Such requirements are generally in the range of about 10 ppm to 500 ppm of sulfur in the fluid stream. If the fluid stream is to be burned as a fuel, removal of sulfur from the fluid stream can be necessary to prevent environmental pollution. If the fluid stream is to be processed, removal of the sulfur is often necessary to prevent the poisoning of sulfur sensitive catalysts or to satisfy other process requirements.
A variety of methods employing regenerable, solid contact materials are known for removing sulfur from a fluid stream when the sulfur is present as hydrogen sulfide. For example, U.S. Pat. No. 4,088,736 discloses a composition comprising zinc oxide, alumina, and a Group IIA metal which is an effective absorbing composition for hydrogen sulfide and which possesses the property of being regenerable to the original absorbing composition state in the presence of oxygen when fully sulfided.
Although the absorbing compositions employed in such methods may effectively absorb hydrogen sulfide from a fluid stream containing hydrogen sulfide, it has been found that many of these absorbing compositions effectively oxidize significant amounts of hydrogen sulfide to sulfur dioxide. The resulting sulfur dioxide is not absorbed by the absorbing compositions and, thus, passes unabsorbed through the contact material. In view of the fact that environmental concerns are focused on the total amount of sulfur contained in an effluent stream, and not just the amount of hydrogen sulfide, passing sulfur dioxide through the contact material and out to the environment is not acceptable under current environmental standards.